1. Field of the Invention
This invention relates to a photosensitive resin having high sensitivity and high resolution performances to electromagnetic waves such as ultraviolet light, far ultraviolet light, vacuum ultraviolet light and X-radiation, or charged particles such as electron rays and ion beams, a resist composition making use of such a photosensitive resin, a pattern formation method making use of the resist composition, and also a device produced by the pattern formation method. This invention relates to an exposure method making use of the resist composition.
2. Related Background Art
In recent years, with a progress of scale-down in semiconductor devices such as integrated circuits and display devices or in masks for exposure, their pattern line width has tendency to be reduced. In microfabrication, light in the region of from near ultraviolet to far ultraviolet is used as exposure light, and processing is carried out in wavelength regions (600 to 248 nm) of such light.
At present, however, the reduction of line width is approaching a limit. For a further reduction of line width, it is attempted to use light having much shorter wavelength. Then, in recent years, lithographic techniques using as an exposure light source an ArF excimer laser of 193 nm in wavelength or an F2 laser of 157 nm in wavelength are gone ahead with development.
Achievement of such a shorter wavelength for the wavelength of exposure light brings about a very important problem that resists have a low transmittance to exposure light to cause a deterioration of pattern resolution performance. Especially in photolithography using the ArF excimer laser as a light source, in view of light transmittance it is very difficult to use novolak resin or polyvinyl phenol having been used in conventional resists, because either has an aromatic ring in the structure and this aromatic ring has a very high light absorption. Meanwhile, the light transmittance to exposure light is known to be greatly improved by the use of a fatty acid polymer.
However, resists making use of such a fatty acid polymer commonly have a poor resistance to dry etching carried out when the substrate is processed after a pattern is formed. Accordingly, resists making use of a polymer having an alicyclic group in the polymer side chain have been brought forth. For example, such resists may include those making use of a norbornene-methacrylate copolymer or adamantyl methacrylate. The resists making use of such polymers are disclosed in, e.g., Japanese Patent Application Laid-Open No. 5-80515 and No. 5-265212.
A photosensitive resin further having an alicyclic group in the backbone chain is also disclosed in J. Photopolymer Science and Technology, 11 (3) 481 (1998).
However, the polymers having an alicyclic group commonly have so low a solubility in solvents and developing solutions that it has been difficult to obtain resists having a high performance or it has been difficult to control molecular weight and molecular weight distribution when the polymers are synthesized.
To solve the above problems, as disclosed in Japanese Patent Application No. 10-24367 it is proposed to solve the above problems by using a polymer represented by the following formula, having a moiety which has an alicyclic group for improving dry-etching resistance and transparency, a moiety which cleaves in the presence of an acid to improve the solubility in developing solutions and a moiety which improves the solubility in solvents. 
An object of the present invention is to solve the problem discussed above, and provide a photosensitive resin having a superior solubility in solvents and a superior dry-etching resistance and enabling easy fabrication of highly integrated semiconductor devices; and a resist composition making use of the photosensitive resin, a pattern formation method making use of the resist composition, a device produced by the pattern formation method, and an exposure method.
To achieve the above object, the present invention provides a photosensitive resin having at least three moieties in the backbone chain, two moieties of which moieties are an alicyclic group moiety and a sulfonyl moiety. The photosensitive resin may further has a vinyl monomer moiety in the backbone chain.
The present invention also provides a resist composition comprising the above photosensitive resin and a solvent for dissolving the photosensitive resin.
The present invention still also provides a pattern formation method comprising the steps of coating the above resist composition on the surface of a substrate to form a resist film, exposing the resist film to light, and developing the resist film thus exposed.
The present invention further provides a device produced by the above pattern formation method.
The present invention still further provides an exposure method of exposing a resist having the above photosensitive resin.
The photosensitive resin of the present invention has a alicyclic group moiety and a sulfonyl moiety which stand copolymerized, and hence responses sensitively upon external stimulation by light to cleave at the part between the both moieties. Also, where the photosensitive resin of the present invention has a vinyl monomer moiety in the backbone chain, the dry-etching resistance is improved.